Chemical Underpinning

If a structure’s foundation soils are too weak to support its weight, SlabJacker can inject the soil beneath the footing to increase its load bearing capacity. Commonly referred to as chemical underpinning or compaction grouting, the system uses high strength polyurethane resin to create solid underpins or a continuous section that will transfer weight down to a more stable foundation. Steel rods can also be embedded into the consolidated soil to provide effective resistance to movement and uplift. The system should be considered in instances where:

  • foundation soils are too weak to support the existing structure and imposed load – If foundation soils have already sunk, chemical underpinning can be used effectively in conjunction with Slab Jacking or Void Filling to provide a total repair
  • additions to a building or a change of use are planned that will increase the load placed upon the foundation
  • foundation soil is unstable and slipping downhill
  • foundation soils are subject to vibration from construction processes, heavy plant, traffic, or seismic activity.

Advantages of Chemical Underpinning

The load bearing strength of chemical underpins is comparable to traditional concrete underpins, but the method of installation and characteristics of the products used give it a distinct advantage in many applications:

  • Installation is fast and our processes cause minimal disruption to daily operations. Our injection resins are fast curing and treated areas can be returned to service almost immediately.
  • Our resins are injected from the surface though specialised grout tubes. No heavy machinery or excavation is required during installation so there will be minimal impact to landscaping.
  • Chemical underpins are lightweight in comparison to concrete so they will not significantly increase the load placed upon foundation soils.
  • Non shrink, stable, and strong in compaction; the performance of our resins will not diminish over time.
  • The cured resins are inert and non-toxic. They will not harm plants and animals or contaminate water.
  • As the cured resins remain slightly flexible, they are resistant to fracture and breaking and are ideal for the stabilisation of buildings subject to vibration.



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